The Model 637 is an exposed-hammer J-Frame with an aluminum alloy frame and stainless steel barrel and cylinder. It combines the weight savings of the Airweight line with the option for deliberate single-action fire, occupying the space between the fully hammerless 642 and the all-steel 60. Type: Revolver Action: Double-Action Caliber: .38 Special +P Capacity: 5 Year introduced: 1996, USA Weight: 15 oz Overall length: 6.31" Status: Active Intended use: Carry, Concealed Carry